Method of firing in furnaces or soaking pits



.l [TED STATES Aorifice METHOD F FIRING IN FURNACES 0R SOAKING PITS Frederick M. Washburn and Roland N. Powel, Chicago, Ill., assignors to International Harvester Company, a corporation of New Jersey Application June 19, 1942, Serial No. 447,664

6 Claims.

This invention relates to a method of firing a furnace. More specically it relates to a method of firing a furnace for soaking ingots.

The usual procedure in soaking ingots, that is, heating ingots to a predetermined temperature, is to bring the furnace containing the ingots to a predetermined temperature and thereafter to hold the furnace at the predetermined temperature for a time toinsure that the ingots have reached that temperature. Normally, fuel required for bringing the furnace up to temperature is considerably greater than that required for maintaining the furnace at the requisite temperature. Thus, if a gaseous fuel is used considerably less volume of fuel per unit of time will be required for the soaking period than for the 'period during which the furnace is brought to temperature. In some instances the volume of fuel required is so small that stratification of the gases in the furnace takes place, the small volume of gas moving only through certain portions of the furnace, and the remainder of the furnace being occupied by dead gas which does not circulate. The result is a non-uniform heating in the furnace and an incomplete heating of some of the ingots. Accordingly, some method must be devised which will assure a suicient volume of gaseous fuel in the furnace to overcome non-uniform heating.

An object of the invention is to provide an improved method of firing,

A further object is the provision of an improved method for firing a furnace for soaking ingots.

According to for ingots is fired by two fuels simultaneously. One fuel such as coke-oven gas has a relatively high heat content per unit volume, and the other fuel such as blast-furnace gas has a relatively low heat content per unit volume. During the period in which the furnace is broughtto the predetermined temperature of soaking, the two gaseous fuels are supplied at relative rates necessary for bringing the furnace to temperature at the desired time. Thereafter the rate of supply of the gas of high heat content such as' coke-oven gas is reduced in proportion to the rate of supply of the gas of low heat content such as blast-furnace gas so that the total volume of gas present per unit of heat developed is higher than it was during the period in which the furnace was brought the present invention, a furnace to the predetermined temperature. Thus, a suflicient volume of gas is maintained in the furnace to prevent stratification of gases therein, in spite of the requirement for lower heat.

In the drawings: A

Figure 1 is a diagrammatic showing of a furnace with pipes for supply of gaseous fuels thereto and control means for regulating the supply of gaseous fuels through the pipe;

Figure 2 shows graphically one method of firing a furnace; and

Figure 3 shows firing a furnace.

The reference character I0 designates a furnace which may be of considerable volume for soaking ingots. In the lower part thereof is a burner II. Extending from the furnace at the burner II is a mixing chamber I 2 in which air and gaseous fuels are mixed. A pipe I3 for air extends from the right of the mixing chamber I2, and from the left thereof extends a duct I4 for a mixture of gaseous fuels. Extending upwardly from the left end of the pipe I4 is a pipe I5 through which the gaseous fuel of low heat value, such as blast-furnace gas, may be admitted, and extending upwardly from another point of the pipe I4 is a pipe I6 through which/ gaseous fuel of a relatively high heat content, such as cokeoven gas, may be admitted. The pipe I5 contains a valve I'I for controlling the passage of gas graphically another method of l therethrough, and the control of this valve is shown schematically as effected byr a motor I8 connected to the valve by an arm I 9 on the valve, an arm 2D on the motor, and a link 2| connecting the arms I9 and 2D. The motor I8 is controlled by conductors 22 coming from a control device 23. Similarly, the pipe I 6 has a valve 24 therein which is controlled by a motor 25 connected to the valve by an arm 26 on the valve, an arm 21 on the motor,

and a link 28 connecting the arms 26 and 21. The motor 25 is controlled by the control device/ 23 through conductors 29 which lead from the control device to the motor. The control device 23 is regulated by a thermcoiple 30 positioned in the furnace and connected with the control device by conductors 3|. The controlmeans just described has been shown only schematically, since, per se, it forms no part of the present invention.

Figure 2 shows graphically one method of firing the furnace. According to this method, the furnace in which ingots to be soaked have been placed is brought to a predetermined temperature of 2400 F. in three hours and thereafter is maintained at 2400 F. for three hours. Blastfurnace gas and coke-oven gas are supplied to the furnace at rates indicated in Figure 2. As shown, the rate for blast-furnace gas is volumes and that for coke-oven gas is volumes. Each of these rates is maintained constant until the predetermined furnace temperature has been reached after three hours. Thereafter the rate of '75 volumesof blast-furnace gas is maintained for about an hour and a half, and during this time the rate of coke-oven is reduced gradually from 20 volumes to zel-tr. For another hour and a half only blast-furnace gas is supplied and this at a rate varying from 75 volumes to 40 volumes. The control device 23, which is actuated by the thermocouple 30 in the furnace l0, will regulate the motors I8 and 25 to regulate the valves l1 and 24 to supply the two gases at the desired rates. The through which this is carried out is not shown, since it forms no part of the present invention. It will be seen from Figure 2 that during the first three hours in which the furnace is being brought to temperature, the rate of supply of coke-oven gas in comparison with the rate of supply of blast-furnace gas is higher than during the hour and a half which follows the arrival of the furnace at the predetermined temperature, for during the following hour and a half the blast-furnace gas is maintainedI at its original constant rate, and the rate of supply of cokeoven gas is gradually reduced to zero. Since coke-oven gas has a considerably higher heat value per unit voiume than does blast-furnace gas, it will be seen that. the heat value per unit of gaseous fuel mixturereaching the furnace is reduced. In this way the rate of heat input to the furnace is reduced as requirement for heat to the furnace is reduced without a material reduction in the total volume of gas supply to the furnace. In the second hour and a half, after arrival of the furnace at the predetermined temperature of 2400", the rate of supply of blastfurnace gas is somewhat reduced as the requirement of heat input to the furnace is reduced.

' However, since during this period only blastfurnace gas is supplied to the furnace, the total volume of gas supplied to the furnace is relatively high, since blast-furnace gas is very low in heat content as compared with coke-oven gas.

Figure 3 shows another modified form of firing the furnace. According to this method, the furnace is brought to the predetermined temperature of 2400 much more slowly, the time being ve hours instead of three hours. For the first exact mechanism two hours of this period, only blast-furnace gas is supplied, the rate being increased relatively rapidly to '70 volumes. Then in the three hour period which follows, coke-oven gas is supplied at a rate which increases gradually to a maximum of 20 volumes. For an hour and three quarters thereafter the rate of blast-furnace gas is maintained at volumes, and the rate of coke-oven gas is reduced gradually from 20 volumes to zero. Then for an hour and a quarter only blast-furnace gas is supplied at a rate diminishing from 70 volumes to 40 volumes. As in the case of the firing method of Figure 2, the heat content per unit of volume of total gas mixture is reduced after arrival of the furnace at the predetermined temperature of 2400", in accordance with the requirement for less` heat input to the furnace. In

Blast-iur- Csegn nace gas, cen't By Peiiccnt Y Volume Volume The coke-oven mately 575 B. t.

gas has heat value of approxiu. per cubic foot as against approximately B. t. u. per cubic foot for the blast-furnace gas. It will be seen that, when the amount of coke-oven gas is reduced after arrival of the furnace at the predetermined soaking temperature of 2400 and the volume of blast-furnace gas is kept constant, the total volume of gas supplied per unit of heat is considerably increased. Thus, for a requirement of lower heat input following the arrival of the furnace at the predetermined temperature, the supplying of a greater amount of blast-furnace gas in proportion to the amount of coke-oven gas will bring about a reduction in the heat input without serious reduction in the total volume of gas supplied. Thus, the non-uniform heating is avoided which so frequently occurred in soaking ingots during the period between the arrival of the furnace at the predetermined temperature and the arrival of ingots from the furnace.

The intention is to limit the invention only within the scope of the appended claims.

What is claimed is:

1. A method of firing a reheating batch-type furnace having considerable space therein and containing objects to be heated to a predetermined temperature, comprising supplying to the furnace a gaseous fuel of a relatively high heat content at a constant rate and a gaseous fuel of a relatively low heat content at a constant rate until the furnace reaches thepredetermined temperature, then supplying to the furnace the gaseous fuel of the relatively low heat content at its constant rate and high heat content at a rate diminishing from its constant rate to zero during a predetermined time, and then supplying to the furnace only the gaseous fuel of the low heat content at a rate diminishing from its constant rate to zero during `a, predetermined time and still maintain a conthe gaseous fuel of the is kept nearly constant\\ the gaseous fuel of relatively low heat content at its maximum rate and simultaneously utilizing a gaseous fuel of a relatively high heat content at a rate rising from a minimum rate to a maximum rate; and maintaining the furnace at the predetermined maximum temperature by utilizing the gaseous fuel of high heat content at a rate decreasing from its maximum rate to zero for a certain period of time and simultaneously utilizing the gaseous fuel of low heat content at its maximum rate, and thereafter utilizing only the gaseous fuel of low heat content at a rate decreasing from its maximum to a minimum.

4. A method as specified in claim 3, the gaseous fuel of high heat content being coke-oven gas, and the gaseous fuel of low heat content being blast-furnace gas.

5. In the firing, by the simultaneous use of a gaseous fuel of a relatively high heat content and a gaseous fuel of a relatively low heat content, of a reheating batch-type furnace containing objects to be heated requiring, because Vof a large heat capacity, bringing the furnace to a predetermined temperature and maintaining the furnace at the predetermined temperature for a certain time for soaking of the objects, the method of preventing during soaking uneven heating of the objects due to the small total volume of gaseous fuel and air required for maintaining the predetermined temperature in the furnace, said method comprising adjusting the relative rates of consumption of the gaseous fuels to make greater, during the maintaining of theC predetermined temperature, the ratio of the rate of consumption of the fuel of low heat content furnace after reaching the predetermined temperature.

6. A method as specified in claim 5, the gaseous fuel of low heat content being blast-furnace gas, and the gaseous yfuel of high heat content being coke-oven gas;

FREDERICK M. WASHBURN. ROLAND N. POWEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,926,714 Culbertson Sept. 12, 1933 2,258,515 Mowat Oct. 7, 1941 2,037,149 Reiner Apr. 14, 1936 1,972,259 Brassert Sept. 4, 1934; 1,944,729 Charlesworth Jan. 23, 1934 1,339,190 Fuller May 4, 1920 

